[llvm] 0f56bbc - [InstCombine] reduce FP-casted and bitcasted signbit check
Roman Lebedev via llvm-commits
llvm-commits at lists.llvm.org
Fri Mar 27 23:26:40 PDT 2020
On Sat, Mar 28, 2020 at 12:34 AM Sanjay Patel via llvm-commits
<llvm-commits at lists.llvm.org> wrote:
>
>
> Author: Sanjay Patel
> Date: 2020-03-27T17:33:59-04:00
> New Revision: 0f56bbc1a5b2ddc881d1c55c9024b9c473dac6f0
>
> URL: https://github.com/llvm/llvm-project/commit/0f56bbc1a5b2ddc881d1c55c9024b9c473dac6f0
> DIFF: https://github.com/llvm/llvm-project/commit/0f56bbc1a5b2ddc881d1c55c9024b9c473dac6f0.diff
>
> LOG: [InstCombine] reduce FP-casted and bitcasted signbit check
>
> PR45305:
> https://bugs.llvm.org/show_bug.cgi?id=45305
>
> Alive2 proofs:
> http://volta.cs.utah.edu:8080/z/bVyrko
> http://volta.cs.utah.edu:8080/z/Vxpz9q
>
> Added:
>
>
> Modified:
> llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
> llvm/test/Transforms/InstCombine/icmp.ll
>
> Removed:
>
>
>
> ################################################################################
> diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
> index 63bf3462faac..62b99e8b8b5b 100644
> --- a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
> +++ b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
> @@ -2760,6 +2760,30 @@ static Instruction *foldICmpBitCast(ICmpInst &Cmp,
> if (match(BCSrcOp, m_UIToFP(m_Value(X))))
> if (Cmp.isEquality() && match(Op1, m_Zero()))
> return new ICmpInst(Pred, X, ConstantInt::getNullValue(X->getType()));
> +
> + // If this is a sign-bit test of a bitcast of a casted FP value, eliminate
> + // the FP cast because the FP cast does not change the sign-bit.
> + const APInt *C;
> + bool TrueIfSigned;
> + if (match(Op1, m_APInt(C)) && Bitcast->hasOneUse() &&
> + isSignBitCheck(Pred, *C, TrueIfSigned)) {
> + if (match(BCSrcOp, m_FPExt(m_Value(X))) ||
> + match(BCSrcOp, m_FPTrunc(m_Value(X)))) {
> + // (bitcast (fpext/fptrunc X)) to iX) < 0 --> (bitcast X to iY) < 0
> + // (bitcast (fpext/fptrunc X)) to iX) > -1 --> (bitcast X to iY) > -1
> + Type *XType = X->getType();
> + Type *NewType = Builder.getIntNTy(XType->getScalarSizeInBits());
> + if (XType->isVectorTy())
> + NewType = VectorType::get(NewType, XType->getVectorNumElements());
> + Value *NewBitcast = Builder.CreateBitCast(X, NewType);
> + if (TrueIfSigned)
> + return new ICmpInst(ICmpInst::ICMP_SLT, NewBitcast,
> + ConstantInt::getNullValue(NewType));
> + else
> + return new ICmpInst(ICmpInst::ICMP_SGT, NewBitcast,
> + ConstantInt::getAllOnesValue(NewType));
> + }
> + }
> }
>
> // Test to see if the operands of the icmp are casted versions of other
>
> diff --git a/llvm/test/Transforms/InstCombine/icmp.ll b/llvm/test/Transforms/InstCombine/icmp.ll
> index b2c6213399b0..41bf661b092e 100644
> --- a/llvm/test/Transforms/InstCombine/icmp.ll
> +++ b/llvm/test/Transforms/InstCombine/icmp.ll
> @@ -3609,9 +3609,8 @@ define <2 x i32> @Op1Negated_Vec(<2 x i32> %x) {
>
> define i1 @signbit_bitcast_fpext(float %x) {
> ; CHECK-LABEL: @signbit_bitcast_fpext(
> -; CHECK-NEXT: [[F:%.*]] = fpext float [[X:%.*]] to double
> -; CHECK-NEXT: [[B:%.*]] = bitcast double [[F]] to i64
> -; CHECK-NEXT: [[R:%.*]] = icmp slt i64 [[B]], 0
> +; CHECK-NEXT: [[TMP1:%.*]] = bitcast float [[X:%.*]] to i32
> +; CHECK-NEXT: [[R:%.*]] = icmp slt i32 [[TMP1]], 0
> ; CHECK-NEXT: ret i1 [[R]]
Not that i disagree with the transform, but why do we want to keep bitcast
instead of producing fp comparison?
We then would want to split this fold:
(bitcast (fpext/fptrunc X)) to iX) < 0 --> (fpext/fptrunc X) < 0
(fpext/fptrunc X) < 0 --> X < 0
> %f = fpext float %x to double
> @@ -3622,9 +3621,8 @@ define i1 @signbit_bitcast_fpext(float %x) {
>
> define <2 x i1> @signbit_bitcast_fpext_vec(<2 x half> %x) {
> ; CHECK-LABEL: @signbit_bitcast_fpext_vec(
> -; CHECK-NEXT: [[F:%.*]] = fpext <2 x half> [[X:%.*]] to <2 x float>
> -; CHECK-NEXT: [[B:%.*]] = bitcast <2 x float> [[F]] to <2 x i32>
> -; CHECK-NEXT: [[R:%.*]] = icmp slt <2 x i32> [[B]], zeroinitializer
> +; CHECK-NEXT: [[TMP1:%.*]] = bitcast <2 x half> [[X:%.*]] to <2 x i16>
> +; CHECK-NEXT: [[R:%.*]] = icmp slt <2 x i16> [[TMP1]], zeroinitializer
> ; CHECK-NEXT: ret <2 x i1> [[R]]
> ;
> %f = fpext <2 x half> %x to <2 x float>
> @@ -3635,9 +3633,8 @@ define <2 x i1> @signbit_bitcast_fpext_vec(<2 x half> %x) {
>
> define i1 @signbit_bitcast_fptrunc(float %x) {
> ; CHECK-LABEL: @signbit_bitcast_fptrunc(
> -; CHECK-NEXT: [[F:%.*]] = fptrunc float [[X:%.*]] to half
> -; CHECK-NEXT: [[B:%.*]] = bitcast half [[F]] to i16
> -; CHECK-NEXT: [[R:%.*]] = icmp sgt i16 [[B]], -1
> +; CHECK-NEXT: [[TMP1:%.*]] = bitcast float [[X:%.*]] to i32
> +; CHECK-NEXT: [[R:%.*]] = icmp sgt i32 [[TMP1]], -1
> ; CHECK-NEXT: ret i1 [[R]]
> ;
> %f = fptrunc float %x to half
> @@ -3648,9 +3645,8 @@ define i1 @signbit_bitcast_fptrunc(float %x) {
>
> define <2 x i1> @signbit_bitcast_fptrunc_vec(<2 x double> %x) {
> ; CHECK-LABEL: @signbit_bitcast_fptrunc_vec(
> -; CHECK-NEXT: [[F:%.*]] = fptrunc <2 x double> [[X:%.*]] to <2 x half>
> -; CHECK-NEXT: [[B:%.*]] = bitcast <2 x half> [[F]] to <2 x i16>
> -; CHECK-NEXT: [[R:%.*]] = icmp sgt <2 x i16> [[B]], <i16 -1, i16 -1>
> +; CHECK-NEXT: [[TMP1:%.*]] = bitcast <2 x double> [[X:%.*]] to <2 x i64>
> +; CHECK-NEXT: [[R:%.*]] = icmp sgt <2 x i64> [[TMP1]], <i64 -1, i64 -1>
> ; CHECK-NEXT: ret <2 x i1> [[R]]
> ;
> %f = fptrunc <2 x double> %x to <2 x half>
> @@ -3672,6 +3668,19 @@ define i1 @signbit_bitcast_fpext_wrong_cmp(float %x) {
> ret i1 %r
> }
>
> +define <4 x i1> @signbit_bitcast_fpext_vec_wrong_bitcast(<2 x half> %x) {
> +; CHECK-LABEL: @signbit_bitcast_fpext_vec_wrong_bitcast(
> +; CHECK-NEXT: [[F:%.*]] = fpext <2 x half> [[X:%.*]] to <2 x float>
> +; CHECK-NEXT: [[B:%.*]] = bitcast <2 x float> [[F]] to <4 x i16>
> +; CHECK-NEXT: [[R:%.*]] = icmp sgt <4 x i16> [[B]], <i16 -1, i16 -1, i16 -1, i16 -1>
> +; CHECK-NEXT: ret <4 x i1> [[R]]
> +;
> + %f = fpext <2 x half> %x to <2 x float>
> + %b = bitcast <2 x float> %f to <4 x i16>
> + %r = icmp sgt <4 x i16> %b, <i16 -1, i16 -1, i16 -1, i16 -1>
> + ret <4 x i1> %r
> +}
> +
> declare void @use_i64(i64)
>
> define i1 @signbit_bitcast_fpext_extra_use(float %x, i64* %p) {
>
>
>
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